Whitefly, Dialeuropora decempuncta (Quaintance rind Baker) (Homoptera: Aleyrodidae) has attained the major pest status in mulberry, causing 24% crop loss by sucking the leaf juice and manifesting leaf curl, chlorosis and sooty mould desease during monsoon season in West Bengal, India. The assessment of economic threshold revel is an essential component for formulating the management practices. Experiments were carried out by inoculating five different densities of whitefly viz.,10, 20, 30, 40 and 50 adults on covered mulberry plants in glass houses. From the findings, it was observed that irrespective of released density, no crop loss was observed in the initial period. But with the passing of days, the percent crop loss was increased rapidly. The linear relationship between percent crop loss and number of adults released was established to highlight the significance of economic threshold. The statistical analysis in the linear form of equation showed that initial population of 10, 20, 30, 40 and 50 whiteflies/plant causes 3%, 12%, 21%, 30% and 40% crop loss in a period of 28 days which is equivalent to 57 kg, 247 kg, 437 kg, 626 kg and 816 kg leaf/acre. Execution of management practices (spray of 0.01% monocrotophos) are economical to the farmer whenever the loss is above 247 kg/acre, but below which application of control measures is not economical. From this study, it can be inferred that the economic threshold level far whitefly is 20 individuals/plant beyond which a farmer has to take appropriate control measures.